1. Field of the Invention
This invention relates to generating a ratio clock signal using a global clock signal. More particularly, this invention relates to generating a ratio clock signal at any integer divided by two of a global clock signal.
2. Description of Background
This application is related to U.S. patent application, filed concurrently with this patent application, entitled “Method for Locally Generating Non-Integral Divided Clocks with Centralized State Machines,” Ser. No. 11/341,038, having William V. Huott, Charlie C. Hwang and Timothy G. McNamara and as named inventors, the entire contents of which are incorporated herein by reference.
It is common for an integrated circuit chip (chip) to operate with multiple different clock speeds. Often, chip architecture allows different regions of the chip to have different clock speeds. To achieve multiple different clock speeds, a chip may employ multiple clock grids throughout the entire chip with each clock grid producing a distinct clock speed. However, employing multiple clock grids creates additional expense for chip production. Higher clock skews between clocks of different clock grids may reduce the maximum clock speed and reduce chip performance. Thus, to keep costs down and keep chip performance up, it has been common practice to use a single clock grid to generate a global clock and obtain different clock speeds by developing ratio clock speeds at a specific ratio to the global clock.
It is common to use external control signals to develop derivative clock speeds at a ratio to the global clock. Additionally, absent external control signals, derivative clock speeds are generally limited to having whole number ratios to the global clock of, for example, 2-to-1, 4-to-1, etc. Generally, there is known in the art circuits which centrally generate clocks with multiple frequencies or phases with multiple phase locked loops, and which use an integral divider. Additionally, complex circuits used to generate derivative clock speeds may create a time delay between the global clock and the derivative clock.
An existing solution is provided in U.S. patent application Ser. No. 11/056,024, the entire contents of which are incorporated herein by reference. This application describes a circuit and power device for a local state machine, which while well suited for its intended purpose, is primarily effective when there are only a few local circuits. However, there are embodiments where a high number of circuits use a non-integral divided clock locally. Thus, there is a need for a more compact solution than that described in U.S. patent application Ser. No. 11/056,024.